The present invention relates to split polymeric sprocket wheels used on rotating power and idler shafts which are essentially inaccessible due to their weight, and/or working environment. More specifically, the present invention relates to improvements in the materials and means of attachment of split sprocket wheels used in chain drive systems used in substantially submerged or otherwise corrosive applications.
One example of a submerged, corrosive environment where split sprocket wheels are employed is in the chain drive system used to power a plurality of sludge collector flights in a circuit around a wastewater settling tank.
Conventional settling tanks employed solid metal sprockets and chains which decayed fairly rapidly in the corrosive wastewater. The metal sprockets were later manufactured in split form to facilitate their replacement without the previously encountered necessity of removing the entire shaft 38 from the tank 10, a costly and time-consuming process requiring heavy equipment.
In recent years, metal chain has been replaced in many tanks with polymeric designs fabricated from glass filled polyester, acetal resin or other plastics in an effort to solve the corrosion problem. This process of substitution of materials requires much more than simply replacing metal with plastic. Polymeric replacement chain must be capable of withstanding significant loading, pulling and compressing stresses from the combined weight of the flights, the trapped sludge and scum, and the drag inherent in a system operating in a tank full of liquid. Consequently, significant development time has been spent on new compounds which are satisfactory replacements for metal in the chain application.
Efforts were also made to manufacture a suitable polymeric substitute for the drive and idler sprockets. Problems occurred because the ideal material had to be strong enough yet not too brittle to be easily cracked nor too soft to be easily deformed. Even materials which satisfied the strength requirements were often subject to deformation when excessive torque was applied to localized areas in the process of mounting the sprockets on the shafts. An example would be in the use of set screws to affix a sprocket hub to a shaft. As a set screw is tightened, the polymeric hub is pulled out of round, resulting in less than total hub/shaft contact, resulting in an insecure mounting for the wheel on the shaft.
Thus, there is a need for a corrosion-resistant polymeric split sprocket wheel for a waste settling tank, which is capable of withstanding the loading stress created in pulling a sludge collector flight chain through a tank filled with wastewater, while also being capable of being disassembled and replaced on site without requiring removal of the main shaft. There is also a need for an apparatus to positively mount polymeric sprocket wheels on these shafts in a manner which will provide positive traction for the shaft yet will not secure the joined portions of the sprocket wheel with so much pressure as to cause deformation of the wheel.
Accordingly, it is a principal objective of the present invention to provide a polymeric split sprocket wheel capable of withstanding significant loading stresses of the type encountered in a wastewater treatment settling tank.
It is another objective of the present invention to provide a polymeric split sprocket wheel designed to be assembled on site without requiring removal of the propeller or idler shafts.
It is a further objective of the present invention to provide a polymeric split sprocket wheel attachment means which effectively secures the joined portions of the split wheel together without causing deformation of the wheel.
It is a still further objective of the present invention to provide a polymeric split sprocket wheel attachment means which effectively secures the joined portions of the split wheel to the rotating shaft without causing deformation of the wheel.